Differential pH-dependent cellular uptake pathways among foamy viruses elucidated using dual-colored fluorescent particles

Background: It is thought that foamy viruses (FVs) enter host cells via endocytosis because all FV glycoproteins examined display pH-dependent fusion activities. Only the prototype FV (PFV) glycoprotein has also significant fusion activity at neutral pH, suggesting that its uptake mechanism may deviate from other FVs. To gain new insights into the uptake processes of FV in individual live host cells, we developed fluorescently labeled infectious FVs. Results: N-terminal tagging of the FV envelope leader peptide domain with a fluorescent protein resulted in efficient incorporation of the fluorescently labeled glycoprotein into secreted virions without interfering with their infectivity. Double-tagged viruses consisting of an eGFP-tagged PFV capsid (Gag-eGFP) and mCherry-tagged Env (Ch-Env) from either PFV or macaque simian FV (SFVmac) were observed during early stages of the infection pathway. PFV Env, but not SFVmac Env, containing particles induced strong syncytia formation on target cells. Both virus types showed trafficking of double-tagged virions towards the cell center. Upon fusion and subsequent capsid release into the cytosol, accumulation of naked capsid proteins was observed within four hours in the perinuclear region, presumably representing the centrosomes. Interestingly, virions harboring fusion-defective glycoproteins still promoted virus attachment and uptake, but failed to show syncytia formation and perinuclear capsid accumulation. Non-fused or non-fusogenic viruses are rapidly cleared from the cells by putative lysosomal degradation. Monitoring the fraction of viruses containing both Env and capsid signals as a function of time demonstrated that PFV virions fused within the first few minutes, whereas fusion of SFVmac virions was less pronounced and observed over the entire 90 minutes measured. Conclusions: The characterized double-labeled FVs described here provide new mechanistic insights into FV early entry steps, demonstrating that productive viral fusion occurs early after target cell attachment and uptake. The analysis highlights apparent differences in the uptake pathways of individual FV species. Furthermore, the infectious double-labeled FVs promise to provide important tools for future detailed analyses on individual FV fusion events in real time using advanced imaging techniques

Selecting the Mutual Arrangement of the Engine and Wing in A Transport Aircraft for Short Take-off and Landing

In order to maintain the competitive advantage of the medium short take-off and landing transport aircraft, the task must be solved of ensuring take-off and landing on the ground runways with a length of 600‒800 m when installing a turbojet engine.When the engines are installed on the pylons under the wing, this is achieved by using a «forced» turn of the jet of engines when the flaps are released at an angle of 60°. We have found the mutual location of the wing and the engine on its stagger, based on the position relative to the construction plane of the wing and the angle of installation. A reciprocal arrangement has been determined, making it possible to maximize the lift force owing to the turn of the jet stream. It has been shown that this achieves the continuous flow around the sections of the flaps when they are deflected at a 60-degree angle.We have analyzed the temperature effect of the jet stream on the mechanization and the aircraft wing at the stages of take-off and landing at different positions of engines under the wing, at different flight speeds and angles of attack. The effect of mechanization on the distribution of jet stream speeds and temperatures has been analyzed. It is shown that decreasing the distance between the engine nozzle and the lower surface of the wing leads to an increase in the angle of the jet stream deviation. We have identified those tail section zones of the flap, which require special execution to operate at temperatures above 400 °C.The impact of the jet stream on aircraft's drag in the cruising configuration has been analyzed, as well as the scheme of engine arrangement on the aircraft's electrically dependent systems. We have shown the absence of the impact of the jet stream on the aircraft's drag in the cruising configuration, the reduction of fuel consumption at cruising modes, as well as the favorable impact exerted on the electrically dependent systems due to the significant reduction of gas-dynamic losses along the power plant tract.Ways to modernize the transport aircraft type of An-70 have been proposed to ensure its superiority in its clas

Selecting the Mutual Arrangement of the Engine and Wing in A Transport Aircraft for Short Take-off and Landing

In order to maintain the competitive advantage of the medium short take-off and landing transport aircraft, the task must be solved of ensuring take-off and landing on the ground runways with a length of 600‒800 m when installing a turbojet engine.When the engines are installed on the pylons under the wing, this is achieved by using a «forced» turn of the jet of engines when the flaps are released at an angle of 60°. We have found the mutual location of the wing and the engine on its stagger, based on the position relative to the construction plane of the wing and the angle of installation. A reciprocal arrangement has been determined, making it possible to maximize the lift force owing to the turn of the jet stream. It has been shown that this achieves the continuous flow around the sections of the flaps when they are deflected at a 60-degree angle.We have analyzed the temperature effect of the jet stream on the mechanization and the aircraft wing at the stages of take-off and landing at different positions of engines under the wing, at different flight speeds and angles of attack. The effect of mechanization on the distribution of jet stream speeds and temperatures has been analyzed. It is shown that decreasing the distance between the engine nozzle and the lower surface of the wing leads to an increase in the angle of the jet stream deviation. We have identified those tail section zones of the flap, which require special execution to operate at temperatures above 400 °C.The impact of the jet stream on aircraft's drag in the cruising configuration has been analyzed, as well as the scheme of engine arrangement on the aircraft's electrically dependent systems. We have shown the absence of the impact of the jet stream on the aircraft's drag in the cruising configuration, the reduction of fuel consumption at cruising modes, as well as the favorable impact exerted on the electrically dependent systems due to the significant reduction of gas-dynamic losses along the power plant tract.Ways to modernize the transport aircraft type of An-70 have been proposed to ensure its superiority in its clas

Conformational dynamics of special nucleic acid structures studied by single molecule FRET.

between multiple chromophores studied b